<?php
class Person {
    public static $type='人类';
    public function show1() {
        //var_dump($this);		//object(Student)#1 (0) { }
        //echo self::$type,'<br>';	//人类
        echo static::$type,'<br>';			//学生   延时绑定
    }
}
class Student extends Person {
    public static $type='学生';
    public function show2() {
        //var_dump($this);		//object(Student)#1 (0) { }
        //echo self::$type,'<br>';	//学生
        echo static::$type,'<br>';			//学生
    }
}
//测试
$obj=new Student();
$obj->show1();
$obj->show2();